The present invention relates to a time-division multiplex transmission network system applicable to an automotive vehicle. Such kinds of time-division multiplex transmission network systems are exemplified by a Japanese Patent Application Unexamined Open No. Sho. 51-14589.
The disclosed system in the above-identified document will be described with reference to FIG. 1. A power supply line 10 is connected to a DC power generator 12 and to a vehicle battery 14. The power supply line 10 is also connected to a plurality of transmission stations 16-1, 16-2, . . . and a plurality of reception stations 18-1, 18-2, . . . . Each transmission station 16-1, 16-2, . . . , is furthermore connected to switches 20-1, 20-2, . . . , such as switches for a wiper, headlights, and so on. In addition, each reception station 18-1, 18-2 is furthermore connected to actuators as loads 22-1, 22-2, . . . which actuate in response to switching actions of the corresponding switches.
A data on switching information from the transmission stations 16-1, 16-2, . . . to the reception stations 18-1, 18-2, . . . is transmitted via a common data transmission line 24 in a time-division multiplex transmission mode. The above-described time-division multiplex transmission of data is carried out in accordance with a series of clock pulses generated by means of an address clock generator 26. The series of clock pulses is sequentially sent to the stations, i.e., transmission stations 16-1, 16-2, . . . and reception stations 18-1, 18-2, . . . , respectively. Consequently, the data is transmitted from one of the transmission stations 16-1, 16-2, . . . and one or plural numbers of the reception stations 18-1, 18-2, . . . which are specified by means of the series of clock pulses for each allocated time slot defined by each period of the clock pulses so that the actuators 22-1, 22-2 are automatically operated according to an on-and-off state of the corresponding switches 20-1, 20-2.
In the above-described construction of the time-division multiplex transmission system applied to the vehicle disclosed in the above-identified Japanese document, each period of the series of clock pulses generated by the address clock generator 26 is extended by using a switch 30 such as an ignition switch which is usually turned off when the vehicle is parked, since an electric power of the battery 14 is still consumed with the generation of electric power by means of the generator 12 stopped.
This causes the electric power consumption of the battery 14 to be suppressed so that an excessive discharge of the battery 14 can be prevented.
However, although the power consumption of the battery 14 can be reduced by the extension of the period of the series of clock pulses, it is difficult to further reduce the power consumption of the battery 14.
In addition, in a case when the data having plurality of bits is transmitted between a pair of the transmission and reception stations, within one time slot, each transmission station 16 (or each reception station 18) requires an independent clock generator which generates a clock pulse train signal in synchronization with which the data having the plurality of bits is transmitted (or received), as exemplified by a U.S. patent application Ser. No. 592,547 filed on Mar. 23, 1984, now pending (which corresponds to a Japanese patent Application Serial No. Sho. 58-105541 filed on June 13, 1983). In this case, since a ratio of the power consumption by these clock generators installed in the individual transmission stations (reception stations) to the whole power consumption of the battery is increased, the whole power consumption of the battery cannot remarkably be reduced.